There exist fast-in-slow-out (FISO) analog memories for acquiring analog data and a very rapid rate and then reading out the data at a much slower rate. One example of such a FISO analog memory is described in Saxe, U.S. Pat. No. 4,271,488. Another example is described in Saxe, U.S. Pat. No. 4,144,525.
Such FISO analog memories are limited in the amount of data they can contain. Once the memory is filled, acquisition must stop while the memories are read and the data are processed.
Therefore, existing FISO analog memories allow data to be acquired at varying sample rates or "decimation" rates. At a slower sample rate, that is, a higher decimation rate, less data is acquired per unit of time. While this can increase the time record available, it also decreases the effective bandwidth of the data, and therefore increases the possibility of aliasing.